Heat-recoverable articles, such as heat-recoverable sleeves, are useful for forming enclosures around substrates to be insulated or protected because the article can be made large enough for easy installation, and then recovered into close contact with the substrate. Close tolerances in manufacture and craft-sensitivity in installation can therefore be avoided.
A heat-recoverable article is an article the dimensional configuration of which may be made substantially to change when subjected to heat treatment.
Usually these articles recover, on heating, towards an original shape from which they have previously been deformed but the term "heat-recoverable", as used herein, also includes an article which, on heating, adopts a new configuration, even if it has not been previously deformed.
In their most common form, such articles comprise a heat-shrinkable sleeve made from a polymeric material exhibiting the property of elastic or plastic memory as described, for example, in U.S. Pat. Nos. 2,027,962, 3,086,242 and 3,597,372. As is made clear in, for example, U.S. Pat. No. 2,027,962, the original dimensionally heat-stable form may be a transient form in a continuous process in which, for example, an extruded tube is expanded, whilst hot, to a dimensionally heat-unstable form but, in other applications, a preformed dimensionally heat stable article is deformed to a dimensionally heat unstable form in a separate stage.
In the production of heat recoverable articles, the polymeric material may be cross-linked at any stage in the production of the article that will enhance the desired dimensional recoverability. One manner of producing a heat-recoverable aricle comprises shaping the polymeric material into the desired heat-stable form, subsequently cross-linking the polymeric material, heating the article to a temperature above the crystalline melting point or, for amorphous materials the softening point, as the case may be, of the polymer, deforming the article and cooling the article whilst in the deformed state so that the deformed state of the article is retained. In use, since the deformed state of the article is heat-unstable, application of heat will cause the article to assume its original heat-stable shape.
In other articles, as described, for example, in British Pat. No. 1440524, equivalent to U.S. Pat. No. 4,168,192, tubular member is held in a stretched state by a second member, such as an inner tubular member, which, upon heating weakens and thus allows the elastomeric member to recover.
Heat shrinkable sleeves find many applications, especially in the connection and termination of wires, cables and pipes. However, there are other applications where it is desirable to provide a connecting, insulating, or protective heat-recoverable member for elongate objects such as cables and pipes where the ends are not accessible, or if they are accessible, where it is undesirable to disconnect or otherwise to displace them. For such applications the so called "wrap-around" sleeves have been developed. Basically, they are heat-recoverable sheets which can be wrapped around the substrate to form a generally tubular shape and which in general are provided with fastening means for holding them in the wrapped-up configuration during recovery. Typically such fastening means are mechanical and comprise, for example, rigid clamps, pins or channel members which co-operate with suitably shaped moulded or extruded protuberances adjacent to the overlapping edges of the recoverable sheet. Various types of fastening means are described, for example, in U.S. Pat. No. 3,379,218 and British Pat. Nos. 1155470, 1211988 and 1346479 equivalent to U.S. Pat. Nos. 3,455,336, 3,542,077 and 3,770,556, respectively. In other applications, however, the sheet may be held in the wrapped-up configuration during recovery by means of an adhesive which may, in some cases, be applied on site.
Heat recoverable sleeves have been successfully employed in many fields of application. However, when two or more substrates such as supply lines, for example cables or pipes, are joined so as to form a connection, problems may arise in obtaining an adequate seal, for example at the outlet of a heat recoverable enclosure. Amongst areas in which this problem is typically encountered there may especially be mentioned the outlets of the splice cases described and claimed in British Pat. equivalent to U.S. Pat. No. 4,142,592, 1401167 and the duct seal devices described and claimed in British Pat. No. 1594937, equivalent to U.S. Pat. No. 4,268,041.
One effective solution for tubular sleeves has been to use moulded heat-shrinkable parts provided with preformed outlets for the individual supply lines. However, in general such moulded parts have to be made to suit a specific application. Their versatility has been improved by the use of end caps which seal outlets which are not needed in a specific operation, as described and claimed in British Pat. No. 1594693 but they are nonetheless expensive and thus economically infeasible in many routine applications.
Another, less expensive, solution which has frequently been employed is to use mastic tape to seal the gap between the supply lines so that, on recovery, a proper encapsulation is formed at the end of the heat-recoverable part. However, the use of such tape requires skill on the part of the installer and the method is not applicable to large parts. In addition, the mastic may degrade the overall performance of products which are provided with an inner lining or coating of a hot-melt adhesive.
In British Pat. No. 1604981, equivalent to U.S. Pat. No. 4,298,415, (the disclosure of which is incorporated herein by reference) an effective branch-off is obtained by forming the individual outlets by means of a suitably shaped clip made from a relatively rigid material. In accordance with the invention therein described there is provided a method of forming a branch-off seal between a heat-shrinkable sleeve and at least two substrates such as supply lines, which comprises the steps of (a) positioning a clip having at least two elongate legs over the outer surface of the heat-shrinkable sleeve at the end thereof so as to form at least two terminal conduits; (b) positioning the substrates within the conduits; and (c) applying heat so as to effect shrinkage and to form the desired seal. Steps (a) and (b) may be effected in either order or simultaneously, for example in many cases the clip will be pushed into place after the sleeve has been positioned around the substrates.
In its simplest form the clip used in the invention of British Pat. No. 1604981, equivalent to U.S. Pat. No. 4,298,415, is U-shaped and its two legs are slid over the outer surfaces of the pinched together heat-recoverable sleeve or wrap-around sleeve, or over the surfaces of the heat-recoverable sleeve or wrap-around sleeve and another co-operating surface. However, in preferred embodiments the clip has three legs and the inner leg passes into the heat-recoverable sleeve whilst the outer legs pass outside it; in this way each of the two layers of the heat-recoverable material is pinched between an inner leg and an outer leg. The inner leg may be contoured so as to reduce the possibility of the clip "milking-off" during recovery, and advantageously comprises a hot-melt adhesive which flows during recovery to seal the gap between the conduits which have been formed.